1. Field of the Invention
This invention relates to techniques for the suppression of electrostatic discharge (ESD) and electromagnetic interference and in particular the design of printed circuit board assemblies for the burn-in process during the conducting of life-time qualification testing of integrated circuits (IC) modules that will suppress ESD and EMI.
1. Description of Related Art
Many of the failures that may occur in IC modules can be stimulated to occur sooner by exposing the IC modules to elevated temperatures and power supply voltages. After the completion of manufacture of IC modules, the IC Modules are often "burned-in," where the IC modules are placed in a chamber for exposure to elevated voltage and temperature. The period of the burn-in is usually on the order of 8 to 1000 hours, dependent on the objective of the qualification process. Of the IC modules input terminals are stimulated with operating signals in the meanwhile these terminals are monitored for operation to detect the exact time of failure.
During the preparation for the burn-in handling there is an opportunity for the IC modules to be exposed to ESD voltages and to EMI sources. The ESD voltages could destroy the IC modules and the FMI sources could corrupt the function of the IC modules during the burnin testing.
The suppression of ESD in the design of printed circuit card retention assemblies is shown in U.S. Pat. No. 5,389,001 (Brouschard, III et al.). While U.S. Pat. No. 5,383,097 (DeLucia, et al.) teaches a technique for shielding hand-held electronic devices from ESD.
U.S. Pat. No. 5,386,346 (Gleadall) shows a design for a printed circuit card retention assembly for the suppression of EMI emissions. To protect IC's at the circuit level U.S. Pat. No. 5,406,105 (Lee) demonstrates a design for the protection of IC's at the circuit level with an ESD protection circuit.
A burn-in board assembly is shown in FIG. 1. The assembly is to provide a carrier for testing many IC modules. Many burn-in boards are placed in a burn-in chamber to process large volumes IC modules at one time.
A printed circuit board 10 has many IC modules 20 plugged into sockets that are mounted on it. Wiring traces 70, 80 are connected to each IC module 20. The input stimuli wiring traces 70, between the power supply voltage source terminals (+V) 45 and the system ground reference point terminals (GND) 40, provide the operating input signals to the IC modules 20 and the feedback sensing and the output responses from the IC modules 20 are placed on the output response traces 80, that are located, between the +V terminal 45 and the GND terminal 40 on the side opposite the input stimuli traces 70. The ground reference connections for each IC module 20 is connected to the ground wiring traces 75. The voltage supply connection for each IC module 20 is connected to the voltage wiring traces 85.
All of the wiring traces 70, 75, 80, 85 are connected to the connector 30. The connector 30 is coupled to the system ground reference point through connector terminals 40. The connector 30 also is coupled to a power supply voltage source through connector terminals 45. System input stimuli are coupled through the top side of the connector 30 to the input stimuli wiring traces 70, that are located between the +V terminal 45 and the GND terminal 40, and the system feedback sensing and output response monitor is coupled through the connector 30 to the feedback sensing and output response wiring traces 80, that are located between the power supply voltage source terminals (+V) 45 and the system ground reference point terminals (GND) 40.
An aluminum stiffener 50 is attached to the printed circuit card 10 to prevent the printed circuit card for excessive flexing under a high temperature burnin process. The handle 60 is connected to the aluminum stiffener 50 so that operations personnel are able to move the burn-in assembly during preparation for testing, and during post burn-in handling. The handling provides an opportunity for the exposure of the burn-in assembly to ESD voltages and EMI sources, such as the generation of EMI fields during an ESD event.